Copepods (meaning "oar feet") are small, shrimp-like crustaceans that swim in seas, lakes, and ponds. Copepods are very important in the food web since many animals eat them.

There are 10 orders of copepods and over 4500 species; a few orders are free-swimming, but many are parasites (of fish). The free-swimming copepods move through the water in jerky motions by moving their swimming legs.

Anatomy: Copepods have a hard exoskeleton, many legs (used for swimming and gathering food), a segmented body, and jointed appendages. Most copepods are under 1 mm long, but a few oceanic species are over 1/4 inch (1 cm) long. Although they lack compound eyes, these arthropods have a single simple eye in the middle of the head (sometimes it is only present in the larval stage); this simple eye can only differentiate between light and dark. There are two pairs of antennae; one pair is long and one pair is short. Like all crustaceans, copepods molt their exoskeleton as they grow.

Predators: Free-swimming copepods are a component of zooplankton and are eaten by many organisms, including mussels, fish and fish larvae, squid, sea birds, and mammals (like baleen whales and some seals).

Reproduction: The female copepod produces clusters of eggs that she carries in one or two egg sacs that are attached to her adbdomen.